Base metals recovery by adsorption of cyano complexes on activated carbon

ABSTRACT

A recovery method for base metal values (e.g. copper) from ore slurry or aqueous solution, comprising forming a solution of a metal complex (e.g. cyano-copper) having an affinity for adsorption sites on activated carbon, adsorbing the metal complex onto activated carbon, and stripping the adsorbed metal complex by forming a reaction product with said metal complex, the reaction product having no affinity for adsorption sites on activated carbon. A method for recovering base metals and noble metals separately from an ore containing both is also disclosed. The method is carried out in an apparatus comprising a leaching stage (17) and an adsorption stage (221) which may be combined, and an elution column (11). The method and apparatus also provide a mechanism for recovery of activated carbon and cyanide.

This invention relates to a system and method for recovering metal(s)from pulp material which has particular, although not exclusive utility,in the extraction and recovery of noble metals from ores containing thesame.

In this specification, noble metals are defined to include gold, andbase metals are defined to include metals other than gold which arecomparatively aesthetically less valuable, such metals including nickeland copper. In particular, the invention has application in theextraction process of gold from aurous material, commonly known as thecarbon-in-pulp or carbon-in-leach process.

The carbon-in-pulp and the carbon-in-leach process for the recovery ofgold and silver from cyanide leaching of ores is widespread in the noblemetals mining industry. However, existing plants are considerablyexpensive to construct and run, and accordingly any improvement in theefficiency and construction of the plant, and in the method of runningthe same, can lead to major savings in costs.

The carbon-in-pulp (CIP) process or the carbon-in-leach (CIL) processgenerally consists of the steps of feed preparation of the ore to form apulp, leaching with cyanide solution, adsorption of the resultingcyano-gold complex onto activated carbon, stripping the cyano-goldcomplex from the carbon using elution and recovering the gold from theeluate by electrowinning or other suitable process.

The CIP process is characterised by the adsorption stage occurringseparately from the leach stage and the CIL process is generallycharacterised by combining the leaching and adsorption steps or stagesso that these are performed concurrently; both processes having thestripping and recovering steps performed as a subsequent step.

It is an object of certain aspects of the present invention to provide asystem and method which improves the efficiency of a CIP and/or CILprocess by effectively operating or performing the metal stripping stepor stage concurrently with the adsorption step or stage, either as anadjunct to all of the steps of a conventional CIP or CIL plant, or as analternative to such plants.

The presence of various base metals in the ore can also have adetrimental effect of great proportions on the efficiency and economicsof a CIP or CIL process due to the high consumption of cyanide, and areduction in the leaching and adsorption rates and also in the recoveryrate of the noble metals. Furthermore, the presence of a fast leachingand adsorbing base metal such as copper can significantly reduce thecarbon loading capacity for the noble metals, thereby necessitating morefrequent stripping and a higher carbon inventory resulting in higherproduction costs.

Hitherto, known processes for dealing with base metals contained innoble metal bearing ores have concentrated on minimising the formationof copper cyanide complexes during the leach process by such methods asoperating the chemical environment to minimise the formation of basemetal cyanide complexes, or pretreating the ore to render the basemetals relatively inert to cyanide ions so that cyano-base metalcomplexes do not form; or have got around the problem by ignoring it,merely expending larger quantities of cyanide or carbon in order torecover the required noble metals.

Accordingly, it is an object of certain other aspects of the presentinvention to provide a system and method to mitigate the aforementioneddetrimental effects of base metal laden feed and also, in certaininstances, to provide for the recovery of the base metals in a saleableform.

In accordance with a first aspect of the present invention there isprovided a method of recovering base metal values from materialcontaining said base metal values and noble metal values, comprising:

forming an aqueous solution of a cyano-base metal complex and acyano-noble metal complex including a cyano-base metal complex anionanion having the stoichiometry M(CN)_(x) ^(y-), where M is a base metalcation, x is 2 or 3 or 4, and y is 1 or 2 or 3; by adjusting the amountof available cyanide anion to said base metal cation to favour formationof said cyano-base metal complex anion;

adsorbing said cyano-base metal complex onto activated carbon bycontacting said aqueous solution with said activated carbon until asignificant amount of said cyano-base metal complex has been adsorbed;and

stripping said cyano-base metal complex from said activated carbon ascyano-base metal complex for subsequent recovery of the base metalvalues and recovery for re-use of barren activated carbon or partiallystripped activated carbon containing nobel metal values.

Where the base metal is copper, x=2 and y=1. Where the base metal isnickel, x=4 and y=2.

Preferably in the step of forming said solution, said available cyanideis adjusted by adding aqueous cyanide in quantity sufficient to satisfybut not substantially exceed the ratio of x moles of cyanide anions toone mole of available base metal cation, where x is 2 or 3 or 4.

Preferably the step of forming said cyano-base metal complex is carriedout in a chemical environment where the pH is less than or equal to 9.

Preferably the pH is maintained at approximately 8.

Preferably the steps of forming said cyano-base metal complex andadsorbing said cyano-base metal complex are performed concurrently.

Preferably the step of stripping said cyano-base metal complex isperformed by contacting said activated carbon supporting said cyano-basemetal complex, with a further solution of aqueous cyanide at aconcentration sufficient to increase the cyanide mole ratio of saidcyano-base metal complex.

Preferably in the step of stripping said cyano-base metal complex, saidfurther solution of aqueous cyanide is added in quantity sufficient tosatisfy or exceed the ratio of one mole of cyanide anion to one mole ofcomplex anion available on said activated carbon supporting saidcyano-base metal complex.

In accordance a second aspect of the present invention there is provideda method of recovering base metal values and noble metal values from anore containing said two values comprising the steps of:

operating the method as described in said first aspect at parametersfavourable to leaching said base metal values from said ore, andsubstantially unfavourable for leaching said noble metal values fromsaid ore; and

recovering said noble metals values from said ore subsequent to havingremoved said base metal values therefrom.

Preferably the step of stripping said base metal complex is performed ata temperature of less than 45° C.

Preferably the step of stripping said base metal complex is performed ata temperature of less than 40° C.

In accordance with a third aspect of the present invention there isprovided in a carbon-in-pulp or carbon-in leach process for extractingnoble metal values from ores rich in the same, a further process forrecovering base metal impurities contained in said ore comprisingremoving said base metal impurities by operating the method as describedin any said first aspect to treat said ore, before extracting said noblemetal values from said ore.

Preferably the step of stripping said base metal complex is performed ata temperature of less than 45° C.

Preferably step of stripping said base metal complex is performed at atemperature of less than 40° C.

In accordance with a fourth aspect of the present invention there isprovided in a carbon-in-pulp or carbon-in-leach noble metal recoveryplant, apparatus to recover base metal values from pulp materialcontaining same, comprising: input means for receiving loaded carbonfrom an adsorption stage within said leach noble metal recovery plant,said input means being located upstream from any noble metal valuesstripping stage in said noble metal recovery plant; elution means to:

receive loaded carbon from said input means,

elute said loaded carbon with an appropriate eluant, and

produce an elute comprising cyano-base metal values for subsequentrecovery, and produce stripped or partly stripped carbon for recyclingback into said noble metal recovery plant.

Preferably said apparatus further includes a recovery stage to recoversubstantially all of said eluant from said eluate for reuse.

In accordance with a fifth aspect of the present invention there isprovided a method of recovering base metal values from materialcontaining said base metal values and nobel metal values comprising:

forming an aqueous solution of a cyano-base metal complex having anaffinity for adsorption sites on activated carbon, by adjusting theamount of available cyanide anion to said base metal cation in order toform said complex;

adsorbing said cyano-base metal complex onto activated carbon bycontacting said aqueous solution with said activated carbon until asignificant amount of said cyano-base metal complex has been adsorbed;

stripping said cyano-base metal complex from said activated carbon forsubsequent recovery, by altering the chemical environment in order toform a cyanide complex reaction product from said cyano-base metalcomplex and said chemical environment, where said reaction product ischaracterised in having less affinity for adsorption sites on activatedcarbon;

and returning for re-use barren activated carbon or partially strippedactivated carbon containing noble metal values.

Preferably said cyano-base metal complex comprises a complex anionhaving the stoichiometry M(CN)₂ ⁻, where M is a base metal cation, andsaid cyano-base metal complex is formed by adjusting the amount ofavailable cyanide anion to said base metal cation.

In accordance with another aspect of the present invention there isprovided in a system for recovering metal(s) from pulp materialcontaining same having a cyanide leaching stage, carbon adsorption stageand a metal stripping stage, there being provided a preliminarystripping stage for removing metal values from adsorbed metal cyanidecomplexes at the commencement of said adsorption stage comprisingelution means to: (i) receive loaded carbon from said adsorption stage,(ii) elute said loaded carbon with an appropriate eluant, and (iii)produce an eluate containing values of said metal(s) for subsequentrecovery of said metal(s), and stripped or partly stripped carbon forrecycling back into said carbon adsorption stage for further adsorption.

In a preferred form, said preliminary stripping stage is operated toprovide an optimum chemical environment for the desorption and strippingkinetics of certain base metals present in said pulp to remove said basemetals from said adsorption stage at the commencement thereof so thatadsorption can proceed thereafter with substantially base metalimpoverished pulp.

In an alternative preferred form, said preliminary stripping stage isoperated to provide a favourable chemical environment for the adsorptionand stripping kinetics of certain noble metals present in said pulp toremove at least some of said noble metals from said adsorption stage atthe commencement thereof and thus enable recovery of some of said noblemetals at an early stage in said system.

Preferably, in either preferred form, said preliminary stripping stageis operated continuously and concurrently with said adsorption stage.

Preferably, in said alternative preferred form said preliminarystripping stage is operated to provide a suitable chemical environmentfor the adsorption and stripping kinetics of both noble and base metalspresent in said pulp to remove substantially all of said base metals andat least some of said noble metals from said adsorption stage, at thecommencement of, and concurrent with the proceeding of said adsorptionstage, for subsequent recovery of both said noble and base metals at anearly stage in said system.

Preferably, in said alternative preferred form, said preliminarystripping stage includes a metal extraction circuit comprising a basemetal extraction means and a noble metal extraction means, said noblemetal extraction means comprising secondary adsorption means foradsorbing noble metal values from said eluate onto carbon afterextraction of said base metals from said eluate, so that furtheradsorption is performed in an optimum environment for achieving highnoble metal loadings for subsequent recovery thereof.

Preferably, said noble metals include gold and said base metals includecopper.

Preferably, said base metal extraction means uses precipitation andfiltering techniques or alternatively, or additionally, metal selectiveresins or Vitrokele in an ion exchange apparatus to extract base metalsfrom said eluate.

Preferably, said elution means comprises an elution column having anupper open end for receiving said loaded carbon from said adsorptionstage and a lower adjustable outlet for selectively removing stripped orpartly stripped carbon from said column, an inlet port for introducingeluant under pressure towards the lower end of said column, and anoutlet port for removing eluate towards the upper end of said column sothat elution takes place along the column.

Preferably, said eluant is a cyanide solution.

Preferably, said chemical environment for the adsorption and strippingkinetics of said metals is controlled for said base metals bymaintaining a relatively cold elution temperature and for said noblemetals by maintaining a comparatively high elution temperature.

In accordance with yet another aspect of the present invention, there isprovided a system for recovering metal(s) from pulp material containingsame comprising:

a cyanide leaching stage;

a carbon adsorption stage; and

a metal stripping stage including elution means for receiving carbonloaded with said metal(s) at the commencement of said adsorption stage,eluting said loaded carbon with an appropriate eluant and providingeluate containing said metal(s) for subsequent recovery and stripped orpartially stripped carbon for recycling back into said carbon adsorptionstage.

In a preferred form, said elution means is initially operated to providean optimum chemical environment for the adsorption kinetics of said basemetals so that base metals are removed from said system, and issubsequently operated to provide an optimum chemical environment for theadsorption and stripping kinetics of noble metals substantially freefrom competing base metals so that noble metals can be removed from saidsystem.

In an alternative preferred form, said elution means is operated toprovide a suitable chemical environment for the adsorption and strippingkinetics of both noble and base metals present in said pulp to removenoble and base metals from said adsorption stage, at the commencementof, and concurrent with, the proceeding of said adsorption stage, forsubsequent recovery of both said noble and base metals at an early stagein said system.

Preferably, said metal stripping stage is operated continuously andconcurrently with said adsorption stage.

Preferably, said noble metals include gold, and said base metals includecopper.

Preferably, said elution means comprises an elution column having anupper open end for receiving said loaded carbon from said adsorptionstage and a lower adjustable outlet for selectively removing stripped orpartly stripped carbon from said column, an inlet port for introducingeluant under pressure towards the lower end of said column, and anoutlet port for removing eluate towards the upper end of said column sothat elution takes place along the column.

Preferably, said eluant is a cyanide solution.

Preferably, said chemical environment for the adsorption and strippingkinetics of said metals is controlled for said base metals bymaintaining a relatively cold elution temperature and for said noblemetals by maintaining a comparatively high elution temperature.

In accordance with a further aspect of the present invention, there isprovided in a method for recovering metal(s) from pulp comprising thesteps of leaching said pulp with cyanide to produce metal cyanidecomplexes, adsorbing said metal cyanide complexes onto carbon, andstripping loaded metal values from said carbon after adsorption of saidmetal cyanide complexes to recover said metal(s); a further stepcomprising performing preliminary stripping of metal values from saidcarbon at the commencement of the adsorption step, additional to saidstripping at the completion of said adsorption.

Preferably, said preliminary stripping comprises receiving and elutingloaded carbon at the commencement of said adsorption step with anappropriate eluant and producing an eluate containing metal values forsubsequent recovery of said metal(s) and stripped or partly strippedcarbon for recycling back for further adsorption.

In a preferred form, said preliminary stripping is performed providingan optimum chemical environment for the adsorption and strippingkinetics of certain base metals present in said pulp to remove said basemetals during the commencement of said adsorption step so thatadsorption can proceed thereafter with substantially base metalimpoverished pulp.

In an alternative preferred form, said preliminary stripping isperformed providing a favourable chemical environment for the adsorptionand stripping kinetics of certain noble metals present in said pulp toremove at least some of said noble metals during the commencement ofsaid adsorption step so that at least some of said noble metals can berecovered at an early stage in the method.

Preferably, in either preferred form, said preliminary stripping isperformed continuously and concurrently with said adsorption step.

Preferably, in said alternative preferred form said eluate is passedthrough a secondary carbon adsorption step for adsorbing noble metalvalues from said eluate onto carbon for subsequent recovery of saidnoble metal.

Preferably, in said alternative preferred form, said preliminarystripping is performed providing a suitable chemical environment for theadsorption and stripping kinetics of both noble and base metals presentin said pulp to remove substantially all of said base metals and atleast some of said noble metals, during the commencement of, andconcurrent with, the adsorption step for subsequent recovery of bothsaid noble and base metals at an early stage in said method.

Preferably, in said alternative preferred form, said preliminarystripping includes the step of further adsorbing noble metal values fromsaid eluate onto carbon after extracting said base metals from saideluate for recovery, whereby said further adsorption is performed in anoptimum environment for achieving high noble metal loadings forsubsequent recovery thereof.

Preferably, said noble metals include gold and said base metals includecopper.

Preferably, said chemical environment for the adsorption and strippingkinetics of said metals is controlled, for said base metals bymaintaining a relatively cold elution temperature, and for said noblemetals by maintaining a comparatively high elution temperature.

In accordance with yet a further aspect of the present invention, thereis provided a method for recovering metal(s) present in pulp materialcomprising:

leaching said pulp with cyanide to produce metal cyanide complexes;

adsorbing said metal cyanide complexes onto carbon; and

stripping loaded metal values from said carbon at the commencement ofthe adsorption step so that said stripping is performed concurrentlywith the proceeding of said adsorbing.

Preferably, said stripping includes: receiving and eluting carbon loadedwith said metal(s) at the commencement of said adsorption step with anappropriate eluant and producing an eluate containing metal values forsubsequent recovery of said metal(s) and stripped or partly strippedcarbon for recycling back for further adsorption.

In a preferred form, said stripping step comprises:

(i) initially eluting said loaded carbon with an appropriate eluant inan optimum chemical environment for the adsorption and strippingkinetics of said base metals so that base metal values are removed fromsaid system in preference to noble metal values in the resultant eluate,and

(ii) subsequently eluting loaded carbon with an appropriate eluant in anoptimum chemical environment for the adsorption and stripping kineticsof said noble metals substantially free from competing base metals sothat noble metal values are removed from said system for subsequentrecovery.

In an alternative preferred form, said stripping step comprises elutingsaid loaded carbon with an appropriate eluant in a suitable chemicalenvironment for the adsorption and stripping kinetics of both noble andbase metals present in said pulp to remove noble and base metals at thecommencement of the adsorption step and concurrent with the proceedingof said adsorption for subsequent recovery of both said noble and basemetals at an early stage in said method.

Preferably, said metal stripping is performed continuously andconcurrently with said adsorbing.

Preferably, said noble metals include gold, and said base metals includecopper.

Preferably, said chemical environment for the adsorption and strippingkinetics of said metals is controlled for said base metals bymaintaining a relatively cold elution temperature, and is controlled forsaid noble metals by maintaining a comparatively high elutiontemperature.

The invention will be better understood in the light of the followingdescription of several embodiments thereof. The description is made withreference to the accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of an intermediate plant forremoving base metal cyanide complexes from activated carbon in the oreleach/absorption stage in a CIP/CIL plant, according to the firstembodiment;

FIG. 2 is a schematic block diagram of the leach and adsorption stage ofa CIL plant for noble metal recovery incorporating an intermediate plantfor removing base metal cyanide complexes from activated carbon in theore leach/absorption stage showing connection points to the intermediateplant shown in FIG. 1;

FIG. 3 is a schematic block diagram of a CIP/CIL plant for noble metalrecovery incorporating an intermediate plant for removing base metalcyanide complexes from activated carbon in the ore leach/absorptionstage according to the second embodiment; and

FIG. 4 is a schematic block diagram of a CIP/CIL plant for noble metalrecovery incorporating an intermediate plant for removing base metalcyanide complexes from activated carbon in the ore leach/adsorptionstage according to the third embodiment.

In the first embodiment, a plant for removing base metal impurities inthe form of copper ore, from ore stock feed containing noble metalvalues in the form of gold ore is described. Referring to FIG. 1, anelution column 11 is fed loaded carbon over a slurry separation screen13, located at the top of the elution column 11. At the slurryseparation screen 13 carbon is separated from the slurry, the slurrybeing returned to the absorption tank (route not shown). The loadedcarbon is pumped to the slurry separation screen 13 by a pump 15, from aleach adsorption circuit stage 17. The elution column 11 is fed withmade up sodium cyanide solution 19 via a pump 21 into the bottom thereofthrough a diffusing manifold 23. A one-way valve 25 is provided toprevent back-flow from the elution column 11 into the made-up sodiumcyanide solution 19.

A valve 35 is provided for emptying the elution column 11 of stripped(or partly stripped) carbon. A receptacle 37 is shown for collecting thecarbon, although in practice this method of dealing with stripped orpartially stripped carbon would not necessarily be adopted. A variablespeed pump or other method of transport ideally would be provided forremoval of the carbon to the respective part of the plant. The preferredpart of the plant to which this stripped carbon would be transportedwill be determined by the values with which it is loaded, after havinghad the copper values stripped therefrom.

An eluate outlet 39 is provided to transport the pregnant liquor elutedfrom the elution column 11 to a base metal recovery plant 41 for furtherprocessing.

The plant described with reference to FIG. 1 is ideally suited for useas an intermediate plant in an existing CIP/CIL gold recovery plant. Inpractice, the plant of this embodiment could be associated with eachleach adsorption circuit stage in the ore processing plant. The purposeof the intermediate plant is to remove competing base metal cyanidecomplex salts from the carbon in the adsorption stage, in parallel withthe adsorption of ore leaches.

The particular application for which this intermediate plant isenvisaged is where gold bearing ores occur which contain copper ore.Where copper ores occur with gold bearing ores, copper has long been thebane of the mining industry engaged in recovering the gold from the goldore. Copper competes with the gold for adsorption sites on carbon. Inaddition, the adsorbed copper cyanide complex salts have been found tocontribute to the catalysed oxidation of cyanide, thus resulting inlosses of cyanide reagent. Furthermore, without the use of theintermediate plant, the presence of copper cyanide complexes in theleach necessitates the use of more cyanide to maintain satisfactory goldleaching rates. The purpose of operating the intermediate plant asdescribed in parallel with the leach and adsorption circuit is to removethe adsorbed copper cyanide complex salts from the carbon as soon aspossible, thus minimising the contact time in the leach and adsorptioncircuit of the copper cyanide complex salts. The recovery of copperitself can be performed as an additional process, to economic advantage,in addition to the advantage obtained by minimising cyanide and carbonlosses. Furthermore, it is believed that with the copper removed fromthe ore, the processing of the remaining gold bearing ore is able toproceed more quickly.

In the leach stage, the copper readily complexes with cyanide anions toform complex anions Cu(CN)₂ ⁻, Cu(CN)₃ ²⁻, and Cu(CN)₄ ³⁻. Themonovalent ion exists in a low pH environment, up to a pH of 9, or whenthe concentration of free cyanide (CN⁻ or dissolved HCN) is low, whereit may exist at slightly higher pH values. The relationship between theoccurrence of the monovalent anion appears to be interdependent on bothpH and free cyanide concentration. The species of complex anion freelyinter-convert by varying the pH or altering the concentration of freecyanide available. The trivalent complex anion is most common at high pHor high concentrations of available cyanide.

The monovalent complex anion is readily adsorbed onto activated carbon,and is readily desorbed from activated carbon by altering the conditionsof pH and/or available cyanide, making elution the ideal route forrecovering the complex ionic values and recovering the activated carbonfor reuse in the plant, as the divalent and trivalent complex anionsonly weakly adsorb onto activated carbon.

The monovalent cyano-copper complex species have been found to competeso strongly for adsorption sites on activated carbon, that adsorbed goldcan be displaced from adsorption sites thereby. However, in practice,some gold values will adsorb onto the activated carbon, and pass throughthe elution column with the adsorbed cyano-copper complexes.

The elution column operates at a low temperature, and has found toeffectively operate at a temperature up to 45° C., however any ambienttemperature up to 40° C. is preferred, to minimise the chance of anyloaded gold being desorbed from the activated carbon, with the desorbedcyano copper complex species. At this temperature, during the elution,the gold remains on the activated carbon, whilst the copper cyanidecomplex is desorbed from the carbon and transported as eluate, away fromthe elution column 11. The copper cyanide complex eluate can then besubjected to a suitable process for recovering the copper from thecopper cyanide complex. A suitable process for doing this includessulphidation by addition of suitable reagents such as sodium or ammoniumsulphide, sodium or ammonium bisulphide, or hydrogen sulphide gas,together with a mineral acid for pH adjustment. The copper sulphideprecipitate can then be filtered from the effluent liquor, and then analkali such as sodium hydroxide injected into the filtrate to recoverthe sodium cyanide for reuse in the intermediate plant.

Referring to FIG. 2, the preferred manner of putting the invention intouse, as an adjunct plant for removing copper values from gold bearingores in a carbon-in-leach process, comprises the elution column 11 whichis fed loaded carbon in the same manner as shown in FIG. 1, withreference to the description above, by a pump 15. The leach adsorptioncircuit stage 17 forms the leach and adsorption stages of the adjunctplant, and is a carbon-in-leach process, itself. The leach adsorptioncircuit stage 17 is essentially similar to the carbon-in-leachadsorption circuit stage 217 which is employed for the CIL goldextraction plant (not shown).

The leach adsorption circuit stage 17 of the intermediate plantcomprises, in this embodiment, two separate stages 219, each of whichhas a adsorption vessel 221 containing activated carbon. In otherembodiments, however the leach adsorption circuit stage comprises morethan two separate stages. The stage 219 has an ore slurry feed 223,through which unprocessed ore is fed to the system. The ore is cascadedthrough subsequent stages of the leach adsorption circuit stage 17, andon into the gold CIL plant 217, through its stages 219b. Each stagecontains a solution of sodium cyanide, the stages 219 of the leachadsorption circuit stage 17 being maintained at a pH of less than 9 andpreferably 8, and with an available cyanide concentration sufficient toform the monovalent cyano-copper complex anion, to consume all of thecopper in all stages 219 of the leach adsorption circuit stage.

Barren activated carbon is fed through the inlet carbon feed 225, intothe adsorption vessel 221a, where an initial amount of monovalentcyano-copper anions are absorbed, after which it is transferred to theadsorption vessel 221 contained in the stage 219a, before beingtransferred to the elution column 11 of the intermediate plant. It hasbeen found, that in practice, gold will load on to the activated carbon,in the intermediate stage, which will remain on the activated carbonproviding that the elution temperature is kept below 45° C. The upperoutlet 229 of the elution column will transport cyano-copper complexesfor further processing to recover both of the copper, and the cyanidefor reuse in the CIL plant.

Essentially the gold CIL plant 217 operates as a separate plant to theintermediate plant. However, the carbon which is still loaded with gold,which leaves the elution column lower outlet 227 may be fed into anappropriate stage 219b of the gold CIL plant 217, for loading furthergold values thereon. The particular stage 219b to which this gold loadedcarbon is fed should be determined by analysing the amount of goldpresent on carbon in adsorption vessels in the gold CIL stage, andfeeding it into the adsorption vessel which has gold loadings which aresimilar to that obtained from the elution column lower outlet.

The intermediate plant ore output 231 is fed into the first stage 219 ofthe gold CIL plant 217. The ore contained in the intermediate plant oreoutput 231 is impoverished of copper, thus allowing the gold CIL plant217 to operate at maximum efficiency, with minimum loss of cyanide andactivated carbon. The barren ore finally leaves the gold CIL plant 217through the barren ore output 233, where it is subsequently dumped inthe tailing impoundment.

The stages 219b of the gold CIL plant 217 have adsorption vessels 235which function in the same manner as those adsorption vessels 221 in theintermediate plant. Barren carbon or partially loaded carbon from theelution column lower outlet 227 is fed into the carbon inlet 237, or fedinto an adsorption vessel upstream in the ore flow, as discussed above,in which case barren activated carbon would be fed into the carbon inlet225; whereupon it progresses through the adsorption vessels 235 of thegold CIL plant, until it leaves the loaded carbon outlet 239 for furtherprocessing. The further processing would comprise stripping the loadedcarbon of gold values. The flow of carbon through both plants is in acounter flow configuration to the flow of ore.

In practice, the whole process operates as a continuous process, ratherthan a batch process. The average residence time for reactants in eachstage 219 is variable but is typically one to four hours. Theconcentration of activated carbon used in one trial intermediate plantwould be 15 to 20 g per liter, however, the exact amount would depend onthe amount of impurity being leached from the ore. The number of leachstages 219 will vary, depending on the amount of copper impurity presentin the ore. Two leach stages 219 should be considered to be a minimumrequirement, but three or four stages 219 would be found to be suitablein most applications.

The application of the invention comprising the intermediate plant to acarbon-in-pulp process is essentially the same, except that a separateadsorption column is used, as the adsorption takes place separately fromthe leach.

With certain forms of CIP or CIL recovery plants for gold incorporatingthe base metal recovery method and plant of this invention, the carboncollected from the bottom of the elution column 11 can be returned tothe adsorption stage 17, where further adsorption can take place.

At a certain stage of the process, a point may be reached where, in thepresence of competing copper, the carbon can not support adsorptionbeyond a certain proportion of gold cyanide complex. At this stage, asmuch of the carbon as is practically possible is passed through theintermediate plant to remove the copper cyanide complex salt in theelution column 11, and then instead of being recirculated to the leachand adsorption circuit, is then treated to remove the gold cyanidecomplex. Two methods of treating the gold cyanide complex on the loadedcarbon in conjunction with the intermediate plant hereinbeforedescribed, will now be discussed with reference to the description oftwo further embodiments and FIGS. 3 and 4 of the accompanying drawings.

The gold elution plant consists of an elution column 111 into which isfed carbon loaded with noble metal through a feed inlet 113, located atthe top of the elution column 111. Made up sodium cyanide solution 119is transported by a pump 121 to a diffusing manifold 123 located in thebottom of the elution column 111. A one-way valve 125 is located betweenthe tank containing the made-up sodium cyanide solution 119 and thediffusing manifold 123, to prevent back-flow from the elution column 111when the pump 121 is not running.

A valve 135 is provided to empty the barren carbon from the bottom ofthe elution column 111.

An eluate outlet 139 is provided near the top of the elution column 111for transporting the pregnant liquor containing noble metal cyanidecomplex salt to a holding tank 141, pending recovery of the gold metal.

Referring to FIG. 3, the receptacle 37 accommodates a feeder 151connected to a pump 153 for transporting stripped or partially strippedcarbon selectively to the leach adsorption circuit stage 17 via a valve155.

The plant 41 has an outlet 161 for transportation of noble metal cyanidecomplex salts to a further carbon adsorption stage 163. Further inlets165 are provided to the further carbon adsorption stage 163 to allow theconnection of similar outlets 161 from other intermediate plants andassociated base metal removal plants which operate in parallel withfurther adsorption stages in pulp leach and carbon adsorption circuitsin the ore recovery plant. A pump 167 is provided for pumping the carbonwhich is loaded with gold cyanide complex salts from the further carbonadsorption stage 163, to the feed inlet 113.

In use, the intermediate plant operates as hereinbefore described. Thestripped or partially stripped carbon is returned from the receptacle 37to the adsorption stage 17 via one-way valve 155 until a point isreached where no further gold loading is desired onto the carboncontained with the adsorption stage 17. When that point is reached, theelution column 11 and the made-up sodium cyanide solution is made readyfor elution of gold by bringing the contents up to a higher temperature,around 100° C. The carbon is then introduced into the top of the elutioncolumn 11 via the slurry separation screen 13, and the gold is thenstripped from the carbon within the elution column 11, and passedthrough the plant 41. Providing that the plant 41 uses a selectiveprocess, the cyanide gold complex will pass through to the outlet 161without being affected, however if another method is used to remove basemetals which has effect on noble metals, steps must be taken to divertthe gold cyanide complex around the plant 41. The gold cyanide complexeluate from the elution column 11 is more dilute than the eluate of afully gold loaded carbon, in the instance where a gold cyanide complexdid not have to compete with a copper cyanide complex, and it is forthis reason that the gold cyanide complex is concentrated by passing itinto a further carbon adsorption stage. In the absence of competing basemetal cyanide complexes, the gold cyanide complex will load onto thecarbon to saturation, whereupon it will be eluted in the elution column111 in the standard manner and collected in the holding tank 141, forelectrowinning.

The third embodiment is substantially similar to the second embodimentexcept that the gold cyanide complex concentration stage is notincluded. Referring to FIG. 4, a pump 171 is provided for selectivelypumping stripped or partially stripped carbon from the receptacle 37back to the adsorption stage 17. When the predetermined point isreached, the valve 173 is shut off and the valve 175 is opened, and thepartially stripped carbon is pumped to the feed inlet 113 in the top ofthe elution column 111, where the gold cyanide complex is eluted fromthe partially loaded carbon. As the first elution column 11 will haveacted as a presoak, the elution column 111 uses water heated to close to100° C. as an eluant, supplied from the feed-tank 120 instead of made upsodium cyanide solution 119.

It should be appreciated that the scope of the present invention is notlimited to the specific embodiments described herein. In particular,having described and ascertained the invention, it should be quite clearthat with very minor modification, the plant can be used to recover andconcentrate dissolved copper from tailings water in any type of minewhere copper is present, and is regarded as an impurity. One suchexample of this alternative use would be in a CIP/CIL gold recoveryprocess where divalent or trivalent cyano-copper anion complexes arepresently discarded in the tailings dam at such plants, presenting adifficulty when the water is sought for reuse. By using the plant andmethod of this invention, both pure copper values and cyanide can berecovered. The invention will also have application in removing mercurycontamination from copper ores, by refining the copper ore andseparating it from the mercury values, as mercury has similar propertiesto noble metals in a CIP/CIL process.

I claim:
 1. A method of preferentially recovering base metal values frommaterial containing said base metal values and noble metal values,comprising the steps of:forming an aqueous solution of a cyano-basemetal complex and a cyano-noble metal complex including a cyano-basemetal complex anion having the stoichiometry M(CN)_(x) ^(y-), where M isa base metal cation, x is 2 or 3 or 4, and y is 1 or 2 or 3; byadjusting the amount of available cyanide anion to said base metalcation to favour formation of said cyano-base metal complex anion;adsorbing said cyano-base metal complex onto activated carbon bycontacting said aqueous solution with said activated carbon until asignificant amount of said cyano-base metal complex has been adsorbed;and stripping said cyano-base metal complex from said activated carbonas cyano-base metal complex for subsequent recovery of base metal valuesand recovery for reuse of said activated carbon.
 2. A method ofrecovering base metal values as claimed in claim 1 wherein in the stepof forming said solution, said available cyanide is adjusted by addingaqueous cyanide in quantity sufficient to satisfy but not substantiallyexceed the ratio of x moles of cyanide anions to one mole of availablebase metal cation.
 3. A method of recovering base metal values asclaimed in claim 1 wherein the step of forming said cyano-base metalcomplex is carried out in a chemical environment where the pH is lessthan or equal to
 9. 4. A method of recovering base metal values asclaimed in claim 3 wherein the pH is maintained at approximately
 8. 5. Amethod of recovering base metal values as claimed in claim 1 wherein thesteps of forming said cyano-base metal complex and adsorbing saidcyano-base metal complex are performed concurrently.
 6. A method ofrecovering base metal values as claimed in claim 1 wherein the step ofstripping said cyano-base metal complex is performed by contacting saidactivated carbon supporting said cyano-base metal complex, with afurther solution of aqueous cyanide at a concentration sufficient toincrease the cyanide mole ratio of said cyano-base metal complex.
 7. Amethod of recovering base metal values as claimed in claim 6 wherein inthe step of stripping said cyano-base metal complex, said furthersolution of aqueous cyanide is added in quantity sufficient to satisfyor exceed the ratio of one mole of cyanide anion to one mole of complexanion available on said activated carbon supporting said cyano-basemetal complex.
 8. A method of recovering base metal values and noblemetal values from an ore containing said two values comprising the stepsof:operating the method as claimed in claim 1 at parameters favourableto leach said base metal values from said ore, and substantiallyunfavourable for leaching said noble metal values from said ore; andrecovering said noble metals values from said ore subsequent to havingremoved said base metal values therefrom.
 9. A method as claimed inclaim 8 wherein the step of stripping said base metal complex isperformed at a temperature of less than 45° C.
 10. A method as claimedin claim 9 wherein the step of stripping said base metal complex isperformed at a temperature of less than 40° C.
 11. In a process forextracting noble metal values from ores rich in the same, a furtherprocess for recovering base metal impurities contained in said ore byoperating the method as claimed in claim 1 to treat said ore, beforeextracting said noble metal values from said ore.
 12. A method asclaimed in claim 11 wherein the step of stripping said base metalcomplex is performed at a temperature of less than 45° C.
 13. A methodas claimed in claim 12 wherein the step of stripping said base metalcomplex is performed at a temperature lying of less than 40° C.
 14. Amethod as claimed in claim 1 further including a step of recoveringcyanide solution from said cyano-base metal complex for reuse.
 15. Amethod of preferentially recovering base metal values from materialcontaining said base metal values and noble metal values comprising thesteps of:forming an aqueous solution of a cyano-base metal complexhaving an affinity for adsorption sites on activated carbon, byadjusting the amount of available cyanide anion to said base metalcation in order to form said complex; adsorbing said cyano-base metalcomplex onto activated carbon by contacting said aqueous solution withsaid activated carbon until a significant amount of said cyano-basemetal complex has been adsorbed; and, stripping said cyano-base metalcomplex from said activated carbon for subsequent recovery, by alteringthe chemical environment in order to form a cyanide complex reactionproduct from said cyano-base metal complex and said chemicalenvironment, where said reaction product is characterized in havinglittle affinity for adsorption sites on activated carbon; and returningfor re-use said activated carbon.
 16. A method as claimed in claim 15wherein said cyano-base metal complex comprises a complex anion havingthe stoichiometry M(CN)_(x) ^(y-), where M is a base metal cation, x is2 or 3 or 4, and y is 1 or 2 or 3; and said cyano-base metal complex isformed by adjusting the amount of available cyanide anion to said basemetal cation.
 17. A method as claimed in claim 15 further including astep of recovering substantially all of said cyanide anion from saidcyanide complex reaction product for reuse.
 18. A method as claimed inclaim 16 further including a step of recovering substantially all ofsaid cyanide anion from said cyanide complex reaction product for reuse.